1. Field of the Invention
This invention relates to the cutting of vegetation, and more particularly, it relates to the cutting of vegetation using a flexible, non-metallic cutting line extending from a rotating head into a cutting plane.
2. Description of Prior Art
Various types of devices have been proposed for many years to facilitate the removal of vegetation by mowing, trimming, edging and like operations. In general, these devices have employed a metal blade to effect vegetation removal. Devices of this nature employ prime movers such as electric and gasoline motors. As a result, rotating metal blades can inflict serious and terrible injury upon the user.
In about 1960, there was developed in Europe a trimmer-edger unit employing a flexible polymeric line extending from a rotating head for cutting vegetation. This unit did not work properly because of several defects in structure and operating parameters. In the United States of America, practical vegetation-cutting devices using flexible, non-metallic lines carried upon a rotating head were developed. The devices are shown in U.S. Pat. Nos. 3,708,967, 3,826,068, 3,859,776 and 4,035,912. These patented devices have met outstanding success in the worldwide marketplace. One reason for this success is that these American developments are probably the safest electrical or gasoline-powered tools yet invented for vegetation cutting, edging and trimming operations.
The devices shown in these patents employ a flexible cutting line, such as manufactured from Nylon.RTM. polymer. The cutting line is carried upon a spool internally of a rotating head. When desired to replenish the line or to extend an additional length of it, the rotation of the head was stopped and line manually extended from the head by either (1) uncoiling directly from the head; or (2) unlocking an internal spool, pulling the line from the head to the desired length and releasing the locking mechanism so that the spool was again secured against rotation in the head. These structures in the patented devices have been found to be convenient, simple and reliable. In many of the smaller devices, especially those powered by electric motors, a simpler system to extend the cutting line from the head was desired. The present invention is a device for cutting vegetation in the nature of the patented devices, wherein a simple but reliable mechanism is employed for extending selectively the cutting line in a certain length from the head. More particularly, this novel device or apparatus is simple to operate and has no complicated mechanisms. A speed-sensitive cam within the head controls rotation of an internal spool to provide for selective feeding of cutting line into the cutting plane. A change in speed of rotation of the head activates the cam which allows spool rotation until a certain length of cutting line is fed from the head. Now, the spool is re-locked by the cam to the head. The head is rotated by conventional electric or gasoline motors that rotate the head at speeds reflecting the length of cutting line extending into the cutting plane. For example, an electric motor may rotate the head with a six-inch extended line at 6,000 rpm and at 7,000 rpm with a three-inch extended cutting line length. Thus, the change in speed can be automatically produced by changes in length of the cutting line.